This invention relates to semiconductive devices having increased power and mechanical strength and to methods of making them and it is an object of the invention to provide improved devices and methods of this nature.
More particularly the invention relates to a metallization system on a semiconductive chip, or die, and a method of forming it whereby the semiconductive chip may be metallurgically bonded to the associated terminals. In the case of devices such as zener diodes wherein a semiconductive chip, two terminal slugs and the glass sleeve are assembled together and subjected to a heating cycle for metallurgically bonding the chip to the slugs and for hermetically sealing the slugs to the glass sleeve, the metallurigical bond is formed at the same time as the glass seal. This is achieved without destroying any of the junctions and other properties of the semiconductive chip. The need for placing the chip and the slugs under stress is thus eliminated.
Throughout this patent application the terms semiconductive die, chip, device or the like are used interchangeably without intending any restriction unless specifically pointed out.
While the invention has specific application to diodes such as zener diodes, for example, it will be clear that the invention has application to any semiconductive device wherein a metallization system is utilized for bonding the device to the connecting terminals.
Metallization systems used with zener, and other diodes, have been of the chrome-silver-gold variety wherein subsequent bonding of the die to the lead terminals or slugs has been with lead-tin solders, for example. Such bonding was carried out at relatively low temperatures and of course required a surrounding glass sleeve which would seal to the terminals at about the same low temperatures. Such bonds while quite satisfactory had relatively low strengths and low power carrying capability. Accordingly it is a further object of the invention to provide an improved metallization system of the nature indicated providing greater strength and increased power carrying capability.
Efforts to increase the power carrying capability and mechanical strength, according to the invention, utilizes metallurgical bonding of the die to the terminals. The metallization system for this purpose is carried out at a substantially higher temperature. The latter requires the use of a surrounding glass sleeve which will seal to the terminals at the same relatively high temperature. Moreover, the time-temperature cycle of the metallization system and the glass sealing temperature had to be such as to not damage or destroy the junction or other properties of the semiconductive device. Particularly this is important for low voltage alloy devices. The high temperature time interval thus had to be short.
The aluminum-tin alloy system, according to the invention, has the desired properties including that of enabing rapid cooling of the devices from the glass sealing temperature without either sacrificing the metallurgical bond quality or overstressing the die.
Accordingly, it is a further object of the invention to provide improved devices and methods for achieving these desirable ends.